Stators in rotating electric machines have stator coils accommodated in a plurality of slots that are formed on the inner peripheral side of a stator iron core. Each stator coil is made up of a coil conductor and a stator coil insulating material that covers the coil conductor. The stator coil is produced through winding of an insulating tape, resulting from bonding a fiber reinforcing material such as glass cloth onto a mica sheet, around the coil conductor over multiple turns, and through impregnation with a low-viscosity liquid thermosetting resin composition (insulating varnish) under reduced pressure, followed by press molding so as to yield a predetermined cross-sectional shape. The stator coils are accommodated in two tiers, upper and lower, within the slots. A spacer is inserted between the stator coils, and a wedge for fixing the stator coil is inserted into the open end of each slot, whereby electromagnetic vibration generated by the stator coil during operation of the rotating electric machine is suppressed.
In such stators of rotating electric machines, the coil conductors generate heat derived from load current during the operation of the rotating electric machine. Therefore, this heat is dissipated into a surrounding gas via the stator coil insulating material and the stator iron core. Increasing the thermal conductivity of the stator coil insulating material in this heat transfer path elicits a pronounced effect of enhancing cooling performance, since the thermal conductivity of the stator coil insulating material is much lower than that of the coil conductor or of the stator iron core. It is therefore important to increase the thermal conductivity of the stator coil insulating material in order to increase the output and reduce the size of the rotating electric machine. In particular, higher thermal conductivity in a stator coil insulating material is strongly required in indirectly hydrogen-cooled type rotating electric machines, which are expected to surpass directly water-cooled type rotating electric machines as regards efficiency, operation and maintenance.
Therefore, an insulating tape for rotating electric machine stators has been proposed that has a filler layer containing a scaly hexagonal boron nitride filler of specific orientation ratio, and a mica layer (see Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open No. 2012-175799